The time it takes is one thing, the other I expect is the cost. Is there really an alternative still running ocean transport between Europe and the US? (and not getting on a container ship Michael Palin's Around the World in 80 Days style)
Yeah QE2, costs about the same as an airline ticket last time I checked. For some people who are terrified of flying this is how they manage to visit the US/Europe.
I'm not sure about a regular ocean transport, but you could take a cruise ship between Southampton, UK and Key West, Miami or New Orleans. They're not particularly regular, on top of the additional cost/time constraints.
Cunard. Prices aren't as too terrible, basic rooms are ~£1000 per person one-way.